Define oxidation and reduction in terms of electron transfer and change in oxidation number.

Electron transfer is a fundamental concept in chemistry, especially when discussing redox reactions. To break it down, let's look at a simple reaction between magnesium and oxygen. This reaction involves the transfer of electrons from magnesium to oxygen.

In this example, magnesium starts as a neutral atom. During the oxidation process, it loses two electrons, which transforms it into a magnesium ion with a +2 charge \( \text{Mg} \rightarrow \text{Mg}^{2+} + 2e^- \).
On the other hand, oxygen gains those lost electrons during the reduction process. Oxygen molecules each gain two electrons to form an oxide ion with a -2 charge \( \text{O}_2 + 4e^- \rightarrow 2\text{O}^{2-} \), thus completing the electron transfer.

The takeaway here is that:*Oxidation* involves *losing electrons,* while
*Reduction* involves *gaining electrons.* Understanding this electron transfer is key to grasping how redox reactions work.

Oxidation numbers are used to keep track of electrons in atoms during a chemical reaction. They help us determine which atoms are oxidized and which are reduced.

Oxidation is defined as an increase in oxidation number. Let’s revisit the magnesium and oxygen reaction. Initially, the oxidation number of magnesium is 0 but after oxidation, it changes to +2 \( \text{Mg} (0) \rightarrow \text{Mg}^{2+} (+2) \).

Reduction, on the other hand, is defined by a decrease in oxidation number. In our example, oxygen starts with an oxidation number of 0 and it decreases to -2 upon gaining electrons \( \text{O}_2 (0) \rightarrow 2\text{O}^{2-} (-2) \).

In summary, recognizing changes in oxidation numbers helps us identify which elements are gaining or losing electrons in a reaction.

Redox reactions (short for reduction-oxidation reactions) are chemical processes that involve the transfer of electrons between two substances. Each reaction involves both a reduction process and an oxidation process, making them paired.

For instance, in the reaction between magnesium and oxygen we've been discussing, magnesium is oxidized \(\text{losing electrons}\), while oxygen is reduced \(\text{gaining electrons}\). These two processes are intertwined; one cannot occur without the other.

In a typical redox reaction:

• The *oxidizing agent* is the substance that gets reduced (gains electrons).
• The *reducing agent* is the substance that gets oxidized (loses electrons).

Understanding these roles can help clarify how redox reactions work and why they are essential in both natural processes and industrial applications.